The present invention is related with a photocatalytic reactor based on UV light sources and a supported titanium dioxide (TiO2) based catalyst, and gas ozone for producing hydroxyl radicals, useful for purifying wastewater from confined aquaculture systems, mediated by an advanced oxidative process. The photocatalytic reactor uses a substrate comprising a supported catalyst, which allows the removal of ammonium, nitrite, as well as the removal of water soluble organic matter and water disinfection, it also refers to the method for using and the operation of the same.
A variety of treatments or methods for purifying water, for removing nitrogenous compounds, and for removing the dissolved organic matter, specifically in waste water from the culturing of hydrobiologic species, are known in the prior art, said methods comply independently or in combination of their functions. Among the better known of said methods are composed of the biologic filter purification water system, the foam fractionator's purification water system, the activated charcoal purification water system, the ozonification purification water system, the UV light purification water system, etc.
The following corresponds to a brief description of the above mentioned methods, which are used for wastewater purification, specifically waste water from fish farming.
Biologic Filter Purification Water System:
This system corresponds to an equipment and supplies set, which can have diverse configurations, including from simple gravel filter through complex filtration systems. The most used configuration on intensive aquaculture, is based on the use of nitrifying bacteria, which are duly supported over a specific substrate. Different dimensions and configurations from the bed and/or rotatory types can be found in this system. The system's main features are that the bacteria-supporting medium must allow the growth of microorganisms; that a rigid operation design, i.e. for an established configuration, standard operation variables, are required; and that the system sizing depends on many different variables, such as: dissolved oxygen amount, dissolved and suspended organic material concentration, the density of the hydrobiological specie culture, the biofilter entry and exit flux, the pH value, the dissolved oxygen and ammonia concentration, the water renewal rate, among others. Also, a permanent and continuous flux of the waste water to be treated, is required.
Foam Fractionator Purification Water System:
This system corresponds to a device, using air injection through a diffuser, wherein the air is admixed with the waste water. The oxygen from air oxides and coagulates part of the dissolved organic material, thus forming foam with the organic matter, which subsequently is removed. It is a simple equipment, usually it will be formed by a PVC pipe which, when a pressed air flux entry occurs, it produces turbulence and bubbles, which contact the dissolved organic matter dissolved of the waste water, producing a foam. The main features of this system are that it can have different configurations and designs; and that the system sizing is related, among others, to the inlet air flux, the size of the forming bubble (a mean bubbling caliber of 250 to 350 nm, is recommended), the kind of gas to be used (air, from oxygen to ozone), the air application way, the gas and water flux.
Activated Charcoal Purification Water System:
This system corresponds to a device, which contains a burned plant material bed, having a microcrystalline structure, similar to the graphite one. It is a simple equipment, usually comprising a strong plastic external structure, as a container, wherein the inner part of the container contains the activated charcoal. The waste water to be treated is passed by inside the container, in order to contact with the activated charcoal. The main features of this system are: that it can have different configurations and designs; that the design, depends on the material to be used for manufacturing the activated charcoal, (which finally affects activated charcoal porosity and granulometry); and that the design is established by the required specific surface of the activated charcoal.
Ozonization Purification Water System:
This system consists of a method of using an electrochemical reaction for producing triatomic oxygen molecules, which are formed by the an oxygen molecule excitation, through a high voltage discharge. In an Ozone generator (O3), through the interaction of air with a high voltage field. The system may exhibit different dimensions and configurations. The ozone amount produced is directly related with the generation and the electric discharge ability within the reaction chamber.
UV Light Purification Water System:
This system uses a device for disinfecting water by means of a UV light source. It occurs in a closed and airtight system equipment, wherein the waste water from a culture flows, contacting the UV radiation emitted by the UV lamp. It can have different configurations (number of UV lamps). The design depends on variables, such as: the waste water flux to be treated, the exposition time, the kind of bacteria, or fungus to be treated, the suspended solids concentration (turbidity), among others.
The closed and air-tight equipment, typically called a reactor, is general known and has been used and disclosed in the prior art.
The conventional way of removing the liquid pollulants produced by those intensive aquiculture processes in recirculating systems, considers the use of mechanical filtering for removing the organic material and biological filters for removing the nitrogenous compounds. The system comprising the use of UV light sources, has become the most used water desinfecting system, mainly by the low cost of the same, the treatment time and the absence of any effect over the hydrobiological cultured species. Nevertheless, its efficiency is limited by the presence of suspended solids, which causes a “shadow” or shield effect over bacteria and other microorganisms.
A good development has been achieved by these treatment systems, however, they exhibit some inconveniences, as the operation and maintenance complexity, and the non-efficient filtering, which maintains the hydrobiological species submitted to amonnium and carbon dioxide sub-lethal concentration levels.
In order to stabilize the removing ability, the biological filters require at least a 30 day period, due to the growth of the nitrosome and nitrobacter bacteria, which convert NH4+, and NH3 into NO2, and transform NO2 into NO3* respectively. Additionally, the bacteria must be kept at stable temperature levels, beginning from 24° C. and above the optimal temperature range for the nitrogenous compounds remotion, and a pH range value between 7 and 8. Further, these systems require a minimal dissolve ammonia concentration in water, for avoiding the bacteria inactivation or death, and its filtration efficiency is affected by the existence of the competitiveness for the environmental conditions, of other bacteria degrading organic matter. These facts can turn the biologic filter very unstable, requiring stabilization periods, which can be a risk for the continuity of the hydrobiological species production in the confined culture, causing lethal water quality levels. Likewise, the mechanical filtering systems require sieves for retaining the suspended and dissolved particles, which require constant maintenance of the retained particles removal, in order to maintain the filter's removing efficiency.
The prior art shows a variety of studies related to organic compounds photo-oxidation, mainly for phenolic type compounds (Beltrán y et al., 1995 a,b; Preis et al., 1995; Beltrán et al., 1996 a,b; Pichat et al., 1996), which are used as a model, with the purpose of studying the mechanisms involved in the degradation. Additionally, in said studies it has been demonstrated that the photo-oxidative systems are efficient upon mineralization. Some researchers have used model compounds for studying oxidation, specifically phenolic-chlorine compounds, such as 2,4-dichlorophenol, 2,4-dichloro-phenoxyacetic acid (2,4-D), in order to assess the subsequent application of the system in removing pesticides and herbicides contained in waste water or in the treatment of industrial waste water. The oxidation of these compounds is highly efficient, achieving the complete mineralization of the same, after short treatment periods. The decomposition of black liquor from the kraft pulp process was studied in photocatalytic oxidative systems, said liquor principally contains phenolic compounds derived from lignin high concentrations, wherein it is concluded that the mineralization of phenolic derivatives occurs between 95% and 96%, by means of photocatalytic processes and not by other routes.
The organic compound 4-chlorophenol was used as a model for comparing the efficiency of different AOP systems (Advanced Oxidation Processes), based on the degradation of said compound, demonstrating that an ozone treatment achieved between 59% and 60% of mineraization, during a 6 hour period, or a 4 hour period for an ozone/UV treatment was necessary, and a period of 2.5 hours for the photo Fenton system was necessary, while when the UV/Peroxide system was used, the decomposition was not achieved. On the other hand, regarding the reactivity upon organic compounds, it was demonstrated, that the degradative levels are highly dependent from the chemical structure of substrates, finding that phenol substrate is more reactive than chlorophenol substrate. It has been shown that an effluent with a high content of non biodegradable organic compounds, can be degraded by means of homogenous as well as heterogeneous photo oxidative systems, significantly raising the effluent biodegradability in few minutes of reaction, being the titanium dioxide (TiO2) semiconductor system the most efficient, removing 80% of TOC and diminishing the by 50% the effluent toxicity. On the other hand, a rotatory photocatalytic reactor was designed, which was used for degradating phenol. The degradation efficiency was compared using a mercury lamp with a UV light (wavelength >254 nm), and sunlight. The researchers demonstrated that phenol can be quickly degraded and mineralized in the reactor by the UV lamp, and also, that it can be degraded in relatively short time periods when sunlight is used. The TOC in solution diminishes slowly, nevertheless, the disappearance of phenol occurs faster, which could indicate, that phenol is possibly mineralized into CO2 through intermediate products, which could be useful as a carbon source for microorganisms in the case of a subsequent biologic treatment of the effluent, or simply if the effluent is poured over a water body after the oxidation.
During a textile effluent decomposition, using an immobilized catalyst, a 97-98% of the effluent color reduction was achieved, the total organic carbon (TOC), was reduced by 50%, and the effluent toxicity was reduced by 73%, on a 1 hour treatment period. When comparing the treatment with a suspended catalyst, the latter only achieved a 23% reduction of the total organic carbon (TOC) and a 28% reduction of the effluent toxicity, using the same immobilized catalyst, the decomposition continued using four coloring agents, selected from those that are most used for dyeing in the textile industry: Reactive Orange-16, Reactive Red-2, Reactive yellow-2 and Reactive Blue-19.
For a period of 30 minutes undergoing a photocatalytic treatment with each one of the coloring agents, between 48% and 50% of the organic matter was mineralized and the oxidation capability of the resting compounds, measured as DQO, shows a similar trend. The efficiency of the immobilized catalyst on the photocatalytic decompsition of a herbicide compound, Isoproturon (IP), one of the herbicides most used in Europe.
In collaboration with The Laboratory of Environmental Biotechnology, Institute of Environmental Engineering, the Swiss Federal Institute of Technology, Lausanne, Switzerland and the Plataforma Solar de Almería-Espańa, the efficiency of the immobilized for the photocatalytic decomposition of Isoproturon, one of the most used herbicides in Europe, was tested. The herbicide was totally decomposed and the decomposition efficiency is compared with suspended catalyst efficiency. Further, it was once more demonstrated, that the catalyst efficiency is not reduced when the same is in an immobilized form, also it was established that after 300 hours of experimentation, the activity of the same is not affected.
Reactors applied for the treatment of atmospheres and effluents, are known, as the “Apparatus for High Flux Photocatalytic Pollution Control Using a Rotating Fluidized Bed Reactor” from the Florida Central University.
The U.S. Pat. No. 6,454,937, Horton et. al., the disclosure of which is incorporated herein by reference, describes an UV reactor for purifying water, which operational concept is similar. The reactor comprises UV light sources and ascending guide-pipes for leading the waste water entrance by the lower part of the reactor, wherein once treated the water returns to the exit at the lower part of the reactor by the outer side of the pipes, wherein said part does not operate as a catalyst.
On even an alternative embodiment of the present invention, the method for using the photocatalyst of the present invention further to the radicals produced by the Ozone degradation (TiO2/UV/O3) is disclosed. The state of the art exhibits a plurality of studies related with organic compounds photo-oxidation, principally for compounds of the phenolic type, (Beltrán y et al., 1995 a, b; Preis et al., 1995; Beltrán et al., 1996 a,b; Pichat et al., 1996); which are used as a model, with the purpose of studying the mechanisms involved in the decomposition, and where it has also been demonstrated, that the photo-oxidative systems are efficient regarding the mineralization process. Some researchers, as Prado et al., (1994) and Tang H. (1996), have used compounds as a model for the study of oxidation, specifically phenolic-chlorine compounds, such as 2,4-dichlorophenol, 2,4-dichlorophenoxy-acetic acid (2,4-D), in order to assess the subsequent application of the same in the removal of pesticides and herbicides from waste waters or in the treatment of industrial wastewaters. The oxidation of these compounds is so efficient, achieving the total mineralization, after a short treatment period. In photocatalytic oxidation systems, Mansilla et al., (1994), studied the decomposition of black liquor from the Kraft pulp process, the liquor principally comprises phenolic compounds derived from lignin in high concentrations, where it is concluded that a 96% mineralization of phenolic derivatives occurs due to photocatalysis and not through another route.
Bauer R. and Fallmann H. (1997), used 4-chlorophenol as the model for an organic compound, for comparing the efficiency of different AOP systems upon the decomposition, establishing that it achieves a 60% of mineralization on a 6 hour period during an ozone treatment, or a 4 hour period using the ozone/UV system and a 2.5 hour period for the Photo-Fenton system, while with a UV/Peroxide system no decomposition was achieved. On the other hand, referred to reactivity measures upon organic compounds, it was demonstrated that the decomposition levels are highly dependent from the substrates chemical structure, finding that the phenol substrate is more reactive than the chlorophenol substrate. Yeber et al., (1999), demonstrated that an effluent with a high content of non biodegradable organic compounds, can be decomposed through homogeneous as well as heterogeneous photo-oxidative systems, increasing significantly the effluent biodegradability in few minutes of reaction, being the system that uses semiconductor the titanium dioxide (TiO2), the most efficient, with a 80% removal of TOC and diminishing by 50% the effluent toxicity. On the other hand, Toyoda et al. (2000), designed a rotory photocatalytic reactor, which was used for decomposing phenol. They compared the decomposition efficiency using a UV lamp (wavelength >>254 nm), and sunlight. The authors showed that phenol can be quickly degraded and mineralized in the reactor comprising the UV lamp, and that also it can be degraded in relatively short periods when it is applied with sun light. The TOC value of the solution diminishes slowly, nevertheless, the phenol disappearance is faster, which could indicate that phenol is possibly mineralized into CO2 by means of intermediate products, which could serve as carbon source for the microorganisms in the case of a subsequent biologic treatment of the effluent, or simply if this one is poured in a water body after the oxidation.
On the decomposition of a textile effluent, using the immobiblized catalyst, was possible to reduce the effluent color in 98%, the Total Organic Carbon (TOC) in 50% and the effluent toxicity in 73%, for 1 hour period of treatment.
Comparing the treatment with a suspended catalyst, the latter only achieved a 23% of reduction of the TOC and 28% of the effluent toxicity reduction. Lizama et al., (2001) using the same immobilized catalyst continued the decomposition of four of the most used dyes in the industrial textile dyeing, Reactive Orange-16, Reactive Red-2, Reactive yellow-2 and Reactive Blue-19. After having passed 30 minutes of the photocatalytic treatment with each one of the dyes, the 50% of the organic matter was mineralized and the oxidability of the resting compounds measured as DQO, shows a similar trend. In collaboration with The Laboratory of Environmental Biotechnology, the Institute of Environmental Engineering, the Swiss Federal Institute of Technology, Lausanne, Switzerland and the Plataforma Solar de Almería-España, was tested the immobilized catalyst efficiency on the photocatalytic decomposition of the herbicide Isoproturon (IP), one of the most used herbicides in Europe.
The herbicide was totally degraded and the decomposition efficiency is compared with the efficiency of the suspended catalyst, furthermore, once more, it was demonstrated that the efficiency of the catalyst is not reduced when this one is immobilized, being possible to establish that after 300 experimentation hours, the activity is not affected. These results were published by Parra et al.
On the other hand, the international literature comprises the addition of some substances which are capable of enhancing the production of radicals, and therefore the degradation of pollutants, is the addition of substances in the solution or the dopping of the catalyst with any compound. In 2002, Jaesang L. carried out these type of experiences, wherein he increased in about 20% the dissolved ammonium degradation with TiO2/UV plus 80% air using TiO2 doped with Platinum and injecting N2O during the process. Though, the ammonium degradation is increased, the economic viability (by the use of platinum) and the environmental viability (by the use of N2O, gas from the greenhouse effect) makes difficult its use in a massive way.
However, the use of Hydrogen Peroxide (H2O2) or Ozone (O3) is feasible as a producer of radical under UV light, which have demonstrated their efficiency for degrading organic aromatic compounds, among others (Hapeman-Somich et al., 1992 a,b, Paton et al., 1994, Mokrini et al., 1996).